Information technology is having an important influence on medical imaging. Picture archiving and communications systems (PACS) allow for digital acquisition, image processing and display for a variety of medical imaging modalities in a digital, filmless environment. The advantages promised by digital medical imaging include increased productivity for health care professionals who utilize images and increased flexibility in how medical images are used to improve patient care.
One source of medical images is the detection of x-rays projected through a region of interest in a patient so as to measure the x-ray transmittance with an imaging detector of finite area. Such images are generally referred to as projection radiographic images. After acquisition, the images can be enhanced using digital image processing techniques to maximize the display of diagnostic information in the image. Successful automatic application of the processing, on the capture modality, provides images that are ready for display and serves to increase the productivity of health care professionals as images can be viewed on computer displays or printed for viewing on a light box.
In conventional film-screen radiographs, the visual presentation of radiographs is locked at the time of capture and chemically processed. Unlike conventional film-screen radiographs, digital radiographs may be selectively enhanced after acquisition to provide different appearances. Particular attributes of the image (such as the brightness, latitude, detail contrast, sharpness and the appearance of the noise) can be modified/enhanced. Additionally, computer aided analysis of the image may be performed, such as the computer aided detection (CAD) of lesions in digital mammograms. With multiple uses for medical images, there exists a need to store, retrieve and transmit both enhanced and un-enhanced images. Preferably, such storage, retrieval and transmittal can occur within a PACS system to meet the requirements of all devices in the PACS.
In an open systems environment, such as DICOM (Digital Imaging Communications in Medicine), there are provisions for support of both enhanced and original, or un-enhanced medical images. In particular, the DICOM standard (Digital Imaging and Communications in Medicine PS 3.3-1999, National Electrical Manufacturers Association, 1999) addresses the management of image data which is either enhanced or un-enhanced. The concept is presented in the DX Series Module by the introduction of Presentation Intent Type. This tag may have the value of FOR PRESENTATION or FOR PROCESSING. If the value of the tag is FOR PRESENTATION, the image has been enhanced such that the image may be displayed without additional processing required. If the value of the tag is FOR PROCESSING, the image must undergo additional enhancement processing prior to display and interpretation. The intent of FOR PROCESSING image data is to allow computer-aided-detection processing and to allow more capable systems, which can perform the required enhancement processing, to do so while still using a DICOM image object while also preserving the capability to provide image data that is display-ready by the use of FOR PRESENTATION.
While the DICOM standard provides representations for both enhanced and un-enhanced versions of an image, it does not provide an efficient means to archive and/or transmit images in both un-enhanced and enhanced states. Handling both enhanced and un-enhanced images using the DX series module in DICOM thus adds both complexity and additional image archive storage requirements to a PACS system to manage requests for different versions of the same image.
U.S. Pat. No. 6,301,393 (Spaulding), issued Oct. 9, 2001, relates to representing an image in more than one image processing state using the concept of a delta image to represent the difference between two images. The method disclosed by Spaulding allows a remote user to reconstruct an original un-enhanced image from the combination of an enhanced image and delta image. However, the method of reconstruction disclosed does not account for the delta image file size dependence on spatial filtering operations that may have been applied to generate the enhanced image. As such, the method disclosed by Spaulding is not particularly suited for imaging applications that rely on spatial filtering operations for image enhancement, for example, medical imaging applications.
Accordingly, there exits a need for a method that allows a user to selectively display an enhanced digital image or reprocess an original digital image so that any lost information can be viewed without having to retrieve the large original digital image.